As closures of vial bottles and other containers for preparations, medical rubber closures, each including, for example, a disc-shaped flange portion and a leg portion formed to be continuous to a lower surface side of the flange portion and being inserted in an opening of the container, are being widely used.
Such a medical rubber closure is generally formed of a butyl based rubber, which is excellent in moisture permeation resistance, to prevent the preparation contained in the container from deteriorating due to moisture.
However, a medical rubber closure made of a butyl based rubber is not sufficient in oil resistance and there is thus a problem that it cannot be used, for example, in a case where the preparation is oil based and oil resistance is required.
If, for example, a laminated rubber closure is arranged with which the leg portion is laminated with a coating layer made of a fluorine based resin film, etc., the oil resistance can be improved to some degree even with a rubber closure made of a butyl based rubber. However, there is a problem that when an oil based preparation infiltrates to a lower surface, etc., of the flange portion that is not laminated, the butyl based rubber swells.
Although the oil resistance can be improved, for example, by the medical rubber closure being formed of an oil resistant rubber, such as a fluororubber, fluorosilicone rubber, nitrile based rubber, etc., these oil resistant rubbers are not sufficient in moisture permeation resistance in comparison to a butyl based rubber and there is thus a problem that a sufficient effect of preventing the deterioration of the preparation by moisture cannot be obtained. Even if the leg portion of the medical rubber closure, made of a nitrile based rubber, is coated with the coating layer as described, for example, in Patent Document 1 (Japanese Examined Patent Application Publication No. 07-041065), etc., the moisture permeation resistance is still insufficient and the above problem is not resolved.
In Patent Document 2 (Japanese Examined Patent Application Publication No. 63-43104), it is proposed that the leg portion and the flange portion (closure main body) be formed of an oil resistant fluororubber and a rubber layer, made of a butyl based rubber that is excellent in moisture permeation resistance, be laminated onto the flange portion.
It is considered that with this arrangement, a medical rubber closure having both a high oil resistance due to the fluororubber and a satisfactory moisture permeation resistance due to the butyl based rubber, etc., can be formed.